694 PHILOSOPHICAL TRANSACTIONS. [aNNO I769. 



The concave and convex tools should be ground with fine emery, after you 

 have done one side of the glass, for the oftener these are ground together, you 

 will be the more sure of having the figure true. 



BKD OF THE FIFTY-NINTH VOLUME OP THE OBIGINAJL. 



END OF VOLUME TWELFTH. 



C, and R. Baldwin. Prlatet*, 

 Ntw BriiJjtf-Street, London. 



